Metering pump for liquid products

ABSTRACT

The invention concerns a metering gear pump comprising a set of gears supported and guided solely by the inner peripheral surface of the lobe of the chamber wherein they are housed. They do not comprise any shaft to act as support or guide, thereby enabling to reduce significantly useless spaced difficult to rinse when changing the product to be pumped. For the same purpose, the driving shaft is flexibly connected to the driving gear. Such arrangement provides the advantage of requiring only one single packing seal. Such a pump, connected to a drive motor and an encoder delivering a signal proportional to the number of pump cycles, enables to provide an accurate metering pump for numerous uses.

BACKGROUND OF THE INVENTION

The present invention concerns a metering pump for liquid products.

PRIOR ART

Notably two types of devices for precision metering of liquid productsare known, viz., the motorized gear pump and the flowmeter with flowrate controller. These two types of devices have problems, particularlywhen there is a need for rather rapid change of the liquid product beingmetered, as for instance in robotized installations for car bodypainting. It is necessary, in fact, when the product to be metered israpidly changed, that the metering device is able to be rapidly andeasily rinsed in such a way that during metering of a given product nota particle of the previous product be left in the metering device. Thetwo known types of devices have problems of rinsing caused by difficultaccess for the rinsing or cleaning product or by idle spaces where theproduct to be eliminated may persist as a film or lump. On the otherhand, rinsing that is not optimized will lead to a larger consumption ofthe product as well as to a longer duration of acceptable rinsing.

It is generally admitted that the gear pump represents the more reliableand more precise metering device, but is also the metering device thatis more difficult to rinse in an appropriate manner. A gear pump of thetype considered here comprises at least one driving gear and one drivengear, said gears each being held on a shaft mounted on bearings locatedin the pump body. These bearings give rise to idle spaces difficult torinse and apt to retain pumped product that is degraded, crystallized orhardened. One way to avoid such idle spaces is that of arranging packingseals on each bearing, which means a minimum of four packings per pump.These packing seals are expensive, generally require some maintenance,and are always susceptible to leak.

The document JP 04 041 984 describes a gear pump in which the two gearsare guided by the outer peripheral surface of friction teeth sliding onan inner peripheral surface of the pump chamber. While the problemsmentioned above are partly eliminated by elimination of the gear shafts,the driving gear of this device is set in rotation by a shaft that isrigidly mounted. This has the particular disadvantage of dictating thelateral position of the driving gear, which necessitates a larger pumpchamber and hence additional idle lateral spaces that are difficult torinse.

The patent FR 2 163 935 describes a gear pump in which the driving gearis rotated by a driving shaft fixed in a manner to transmit only arotation torque, the driven gear comprising no support shaft. Thedriving shaft of this pump does not comprise a packing seal, the sealingbeing made by a layer of the pumped liquid. Such disposition does notfacilitate the rinsing of the pump and causes difficulties to use in thecase of frequent changes of the pumped liquid.

The packing described in DE 14 03 912 can under no circumstances besuitable for a pump as proposed here, as it is adapted to a pump havingthe driving heat rigidly fixed to the driving shaft, being disposedbetween two bearings supporting the driving shaft.

It is a first aim of the invention, therefore, to propose a meteringpump for liquid products improved over known metering pumps.

It is a further aim of the invention to propose a metering pump having arinsability distinctly improved over that of known pumps.

Still another aim is that of proposing a metering pump that is able tometer a volume of liquid in precise manner.

These different aims are attained by a metering pump for liquid productshaving the characteristics disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferential embodiment of a metering pump for liquid products isdescribed below, the description to be considered while referring to theannexed drawing comprising the figures in which

FIG. 1 presents a lateral view along a first section of a metering pumpfor liquid products according to the invention,

FIG. 2 presents the same pump along a section in a plane perpendicularto the plane of the section of the preceding figure,

FIG. 3 presents the constituent elements of a metering pump in aschematic way.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows that the body 1 of the pump comprises a bottom plate 10, anintermediate plate 11 and a front plate 12, these three plates herehaving an essentially rectangular external shape and similar dimensions,which are superimposed as can be seen in the figure. Means of attachmentschematically shown at 13 hold these three plates assembled. A seal notshown in the figure secures tight sealing of the contacting faces ofthese three plates.

The intermediate plate 11 seen in elevation in FIG. 2 essentiallyconsists of a plate, rectangular in this embodiment, which comprises achamber 110 consisting of at least two lobes each able to receive a gear30, 31 of a set of gears 3. One can see in FIG. 1 that in the embodimentof the pump represented, chamber 110 reaches entirely across theintermediate plate 1. The intermediate plate 11 additionally comprisesan entry channel 111 for liquid that ends in the chamber 110, as well asan exit channel 112 for liquid that leaves said chamber. The openings ofthese channels can each be arranged on one of the lateral walls of theintermediate plate 11, as shown here, or channels 111 and/or 112 may beextended into either the bottom plate 10 or the front plate 12 whiletheir openings would be located on a periphery of these plates.

The pump additionally comprises a set of gears 3 comprising a drivinggear 30 and at least one driven gear 31 as well as drive organs 4 andpacking seal 5.

The drive organ 4 comprises a motorized organ not represented in thisfigure which ends in a drive shaft 40 that goes through a bearing 120set in the front plate 12. The bearing 120 can be a sliding bearing asshown here or a roller bearing. The end 41 of shaft 40 has a shape suchthat it can be introduced into a recess 300 of the gear 30 ofcorresponding shape so that it will be able to rotate said gear. In thecase represented here, the end 41 and the recess 300 are both hexagonal,but any other shape allowing a rotating drive could be suitable.

One notices in the figure that the gears 30 and 31 are not supported byany shaft, they are guided while rotating, solely by the outerperipheral surface of the teeth in sliding contact on the innerperiphery of the lobes of chamber 10. The lubrication of the surfacesmoving relative to each other is assured by the product being pumped.The shaft 40 that is flexibly connected with the driving gear 30 at itsend 41 only serves to drive said gear while being without any support orguiding function. The shaft 40 or its end 41 can hence only transmit atorque to the driving gear 30 while any other force in whateverdirection is excluded. Since the gears 30 and 31 are no longer guidedlaterally by a shaft, they can now settle laterally under the effect ofpressure of the product being pumped, which acts on their sides. It isthus possible to have a lateral space to both sides of each gear that isas small as feasible, provided a thin sheet of the pressurized productis present that will secure lateral centering of the gear in its lobe.In this way the hollow spaces which would have to be rinsed between twoproducts being pumped are strongly diminished, and only a single set ofpacking seals 5 has to be fixed on the shaft 40.

In known manner, the packing seal 5 can consist of packings, of lipseals or, as shown here, of a mechanical lining. The mechanical lininghas the advantage over other known types of packing seals, of exhibitingthe smallest frictional force in rotation. Therefore, preferably amechanical packing is selected which consists of a sealing ring 50freely mounted around the shaft 40 and able to move axially in a recess121 in bearing 120 while being pressed against the front side of gear 30by an elastic organ, for instance a spring 51, in order to mechanicallysecure a tight seal between the chamber 110 and the shaft 40. An O-ring52 serves as a static sealing barrier in the rear of the sealing ring50. Means represented in the figure at 55 allow rotation of the sealingring to be prevented. Relative to known designs, that of the packingseal 5 here described allows the sealing barrier to be as close aspossible to the end 41 of shaft 40, which substantially contributes to areduction of the hollow spaces that must be rinsed between two productsbeing pumped. It has been mentioned before that the gear 30 waspositioned laterally by the equilibrium of the pressures being exertedon its two sides. Since the side of gear 30 that is linked as describedto the shaft 40 is lower than the opposite side, gear 30 would tend tobe pressed against the inside of the front plate 12. The elastic organs51 will therefore be of a size such that they exert a force able tocompensate the difference between the opposing forces being exerted onthe two opposite sides of gear 30.

Optionally, the packing seal 5 described above is made more complete bya supply 53 of a packing liquid coming from an external reservoir 54.The packing liquid fills the part of recess 121 on the side of O-ring 52that is opposite to that in contact with the liquid being pumped, andthus exerts a counterpressure on this seal so that its sealing will beimproved. A leak of packing liquid in the direction of chamber 110 or aleak of pumped liquid across the seal 52 would lead to a change in levelof the packing liquid in the reservoir 54. By monitoring this level itis therefore possible to detect liquid leaks at the packing seal in anyone direction. The presence of a packing liquid in the hollow parts ofrecess 121 also prevents a condensation and crystallization of the pumped liquid in these hollow parts.

The gear metering pump as described above is thus optimized so as tosubstantially improve its rinsability, by eliminating the hollow spacesto be rinsed between two different p products being pumped d, whichleads to savings of both the rinsing product and rinsing time. Thesimplified pump design which uses a smaller number of pump componentsand requires just a single packing seal reduces by as much themanufacturing cost as well as the risk of leaks, and improves itsreliability.

The above pump can advantageously be used to meter a product beingpumped, the volume of product pumped being essentially proportional tothe number of revolutions of gear 30 or 31. By monitoring this number ofrevolutions it is possible, therefore, to obtain a precision meteringpump. Such a pump is presented schematically in FIG. 3.

One recognizes in this figure the pump body 1 with the driving gear 30being driven by the shaft 40 as described previously. The other end ofshaft 40 is driven by a motor 41, which preferably is an electric motorbut can also be a pneumatic or hydraulic motor or a motor of any otherknown type able to drive the shaft 40. A reducing gear or gear box 42can be arranged on the shaft 40 between the motor 41 and the pump. Therotating speed of gears 30 and 31 of the pump or the volume of liquidpumped are thus equal or proportional to the number of revolutions ofshaft 40 as well as of motor 41. An encoder 43 able to record thisnumber of revolutions can thus send a control signal to a control unit44, for instance an electronic unit containing or not containing aprogrammed microprocessor and able to record this signal and regulatethe pumping process, e.g., by cutting the power supply to the motor 41when the desired quantity of product has been pumped. The encoder can bearranged at the end of the shaft on motor 41, as shown schematically bythe encoder 43 in position A, on shaft 40 in front of or behind thereducing gear 42, if present, as shown schematically in positions B andC, or in the pump itself, as shown schematically at position D. Theencoder 43 is of any known type, optical, inductive, capacitive orother, that is able to record the number of revolutions of the motor 41,of the shaft 40 or of one of the gears 30 or 31, depending on theposition (A, B, C, D) where it has been installed.

The design of the metering pump can be compact, with the motor 41 beingdirectly glued to the pump body 1, or more distributed, with a shaft 40that consists of a flexible drive shaft. Such a pump is advantageouslymounted on a robotic painting arm, for instance in the painting of carbodies, where the pump together with its drive motor can be located inthe mobile part of the robotic arm or, if one wants to minimize themoving masses, the motor 41 can be housed in a part of the base of therobotic arm while the pump body can be located in the mobile end of thearm, while the two elements are linked by a flexible shaft 40. Adistributed design with flexible or rigid drive shaft 40 can also beused in order to obtain an explosion-proof pump where the motor 41 thatmight produce sparks can be remote from the pump body I that could belocated in an explosive atmosphere.

In each of the possible applications of such a metering pump, it will bedetermined by the application considered whether or not a reducing gearor gear box 42 are incorporated, and where the encoder 43 will be placedamong any of the positions described above.

The modular design described allows such a metering pump to be employedin numerous applications, painting, metering of chemical products, foodproducts, pharmaceuticals, etc.

The constituent elements of the pump body 1 as well as the gears 3 andthe packing seal 5 are made of materials which essentially arecompatible with the products being pumped, and which can be metals oralloys, for instance stainless steel, synthetic materials, or ceramics,and these materials may be uncoated or coated with a protecting layer.It is not necessary that the different constituent elements of the pumpbe made of the same material.

A variety of different versions can be envisaged for the design of agear metering pump according to the invention. The pump has beendescribed as having one driving gear and one driven gear; it could justas well comprise a number of driven gears arranged along the peripheryof a driving gear. The chamber of the pump body would then have thenumber of lobes required to receive one gear each. The pump body hasbeen described as consisting of three assembled plates, so as tofacilitate machining of the chamber 110 of the intermediate plate. Itwould also be possible for the intermediate plate 11 to be made as asingle piece together either with the bottom plate 10 or the front plate12. Also, the pump body 1 has been described as being of rectangularshape, but it actually could have whatever shape able to accommodate apumping chamber such as that described. On the other hand, the meteringpump has been described as comprising an electric motor and an encoder,in particular. These two elements could be replaced by a step motor,where the number of steps to be executed is determined by the volume ofproduct to be pumped.

1. A gear metering pump comprising a pump body with a chamber comprisingat least two intersecting cylindrical lobes, a first lobe receiving adriving gear and at least one other lobe receiving a driven gear, saidgears being supported solely by their outer periphery leaning against aninner peripheral surface of each lobe, the driving gear being rotated bya drive shaft, an end of which is introduced into an axial recess ofsaid driving gear, while the shape of said end of the shaft cooperateswith the shape of said axial recess so as to furnish a drive torque tosaid driving gear while the drive shaft constitutes no means of radialor axial support or guidance at all between it and the driving gear, apacking seal mounted on the drive shaft, said packing seal beingpositioned on a surface of a front plate of the pump body that is turnedtoward the driving gear, in the immediate vicinity of the end of saidshaft.
 2. A metering pump according to claim 1, wherein the packing sealcomprises a mechanical gasketing comprising a sleeve arranged in arecess that is coaxial to the drive shaft, said sleeve being pressed byelastic organs against part of a side of the driving gear, said packingseal comprising means able to prevent rotation of the sleeve, and saidsleeve holding an O-ring securing the tight sealing of said coaxialrecess.
 3. A metering pump according to claim 2, wherein the elasticorgans are of a size such that an axial force transmitted by the sleeveis exerted on the driving gear which is able to counterbalance the axialforce in the opposite direction that arises from the difference betweenthe sides of the driving gear on which the pressure of the product beingpumped is exerted.
 4. A metering pump according to claim 2, including asupply of a packing liquid entering said coaxial recess from the side ofthe O-ring that is opposite to the side facing the driving gear.
 5. Ametering pump according to claim 1, associated with an encoding deviceable to supply a signal that is proportional to the number ofrevolutions made by one of the gears of the pump.
 6. A metering pumpaccording to claim 5, wherein said signal is sent to a control unit ableto regulate the pumping process according to the signal received.
 7. Ametering pump according to claim 1, wherein it is associated with amotor able to rotate said drive shaft.
 8. A metering pump according toclaim 7, wherein the drive shaft is a flexible shaft.
 9. A metering pumpaccording to claim 1, wherein it is associated with a robotic armcomprising in particular a fixed base part and a mobile arm.
 10. Ametering pump according to claim 9, wherein said metering pump isassociated with a motor able to rotate said drive shaft, the pump bodyand the motor are mounted on said mobile arm of the robotic arm.
 11. Ametering pump according to claim 9, wherein said metering pump isassociated with a motor able to rotate said drive shaft, the pump bodybeing mounted on the mobile arm while the motor is mounted on the basepart of the robotic arm.